Tomosynthesis imagery is a three-dimensional imaging technique using limited-angle tomography. This technique makes it possible to reconstruct a three-dimensional (3D) volume in slices from a series of bi-dimensional (2D) projection images acquired using different angles of the X-ray tube.
In this volume, the practitioner attempts to identify lesions, such as, in the breast, for example, microcalcification or opacity foci, or, in the lung, potentially cancerous nodules. The practitioner can also seek to repair a bone fracture, for example in the hand or shoulder. These lesions and fractures, visible using a radiography imaging technique, can be generally referred to as “radiological signs”.
In the state of the art, the practitioner examines the volume slice by slice. However, a radiological sign may be distributed over several slices. Consequently, visualizing one given slice of a radiological sign does not allow the practitioner to acquire all of the information relative to this sign. One therefore seeks to be able to visualize the information contained in a volume corresponding to the radiological sign.
It is already known to present practitioners not with only one slice but with a slice corresponding to the integration of several slices, namely an image referred to as a “slab”.
This type of image is not without difficulties, insofar as one strengthens, over the entire image (including in areas located outside the region containing the radiological sign), the superimposed tissue-type artifacts, which is in contradiction with the initial objective of tomosynthesis, namely is to reduce the superposition of tissues with regard to standard 2D radiography.
One purpose of the invention is therefore to propose a display method that is easy for a practitioner to use and that provides the practitioner with as much information as possible on the radiological signs he wishes to analyze.
One example of an imaging system allowing implementation of the invention is diagrammatically illustrated in FIG. 1. We will briefly describe the various devices making up the imaging system, these devices being known to those skilled in the art.
Traditionally, the tomosynthesis device 10 comprises an x-ray source 12 which can be fixed to a support such as a C-shaped arm, a leg or an examining table, which allows movement of the x-ray source 12 in a limited region 14. In FIG. 1, to simplify the illustration, the limited region 14 is flat, but one skilled in the art understands that this schematization is in no way exhaustive and that the x-ray source 12 can, for example, be moved following an arc of a circle or in a three-dimensional region. A collimator can be arranged so as to define the dimensions and shape of the bundle 16 of X rays crossing a region wherein a subject such as a human patient 18 is located. Part 20 of the ray passes through the patient 18, and strikes a detector 22. The detector 22 may include, for example, a plurality of detection elements, corresponding globally to pixels, which produce an electrical signal representing the intensity of the incident X rays. These signals are acquired and processed to reconstruct, in real-time or nearly, an image of the details of the subject. Traditionally, the signals are recorded according to several angles around the patient so as to collect several radiographic views.
The source 12 is controlled by a control unit 24 which provides it with both electricity and control signals for examination sequences. More specifically, the control unit 24 controls the activation and operation of the x-ray source 12 through an X ray control device 26. The control unit 24 also controls the movement of the source 12 in the limited region 14 through a motor control device 28, which moves the source 12 so as to give it the desired position and orientation relative to the patient 18 and the detector 22. Moreover, the detector 22 is coupled to the control unit 24, which controls the acquisition of signals generated in the detector 22. Overall, the control unit 24 controls the operation of the imaging system to carry out examination protocols and to acquire the resulting data.
Moreover, the control unit 24 comprises a data acquisition system 30 which receives the analog signals from the detector 22 and converts them into digital signals for later processing by a processor, for example a computer 32. The computer 32 may comprise—or communicate with—a memory 34 which can store the data processed by the computer 32, or the data to be processed by the computer 32. Any type of memory device accessible by a computer and allowing storage of the desired quantity of data and/or codes can be used. Moreover, the memory 34 may include one or several memory devices, of similar or different types, which can be local or remote relative to the system 10. The memory devices can store data, processing parameters and/or computer programs to carry out the various processes described here.
The computer 32 is typically used to control the tomosynthesis device 10. To this end, the computer 32 is configured to receive commands and acquisition parameters by an operator through a work station 36, traditionally equipped with a mouse, a keyboard and/or other peripherals.
A display screen 38 coupled to the work station allows displaying of the reconstructed image. The image can also be printed using a printer 40, which can be coupled to the work station. Moreover, the work station can also be coupled to a picture archiving and communication system 42 (PACS). The PACS 42 can be coupled to a remote system 44, such that other people can access the image and image data remotely.
Of course, this example is in no way exhaustive and each of the devices presented above can be coupled to other devices, according to the desired implementation.
The data collected by the detector 22 typically undergoes correction, pre-processing and/or calibration in the acquisition system 30 and/or the computer 32 to condition the data so as to visualize the integrals of the attenuation coefficients of the objects analyzed along the rays going from the source to the detector. The processed data, commonly called projection images, can be used by a reconstruction algorithm. In tomosynthesis, one acquires a certain number of projection images, each according to a different angle relative to the subject and/or the detector. Tomographic reconstruction algorithms are well known by those skilled in the art and enable the formation of a three-dimensional image of the volume from the projection images.